Tapped winding arrangement for variable ratio transformer



June 24, 1958 F. J. VOGEL ET AL 2,840,790

TAPPED WINDING ARRANGEMENT FOR VARIABLE RATIO TRANSFORMER Filed June 12, 1956 3 Sheets-Sheet 1 June 24, 1958 F. J. VOGEL ET AL 2,840,790

TAPPED WINDING ARRANGEMENT FOR VARIABLE RATIO TRANSFORMER Filed June 12, 1956 3- Sheets-Sheet 2 JwvmXoA/o ud I). DogaX Jm wwo I. 9110044 J bfoflmg June 24, 1958 F. ,1. VOGEL ETAL 2,340,790

TAPPED WINDING ARRANGEMENT FOR? VARIABLE RATIO TRANSFORMER FiledJune 12, 19ss 3Sheets-Sheet :s

- lllllll United States Patent TAPPED WINDING ARRANGEMENT FOR VARIABLE RATIO TRANSFORMER Fred J. Vogel, Wauwatosa, Wis., and James L. Moon,

Terre Haute, Ind., assignors t0 Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application June 12, 1956, Serial No. 590,936 11 Claims. 01. 336-150) This invention relates in general to variable ratio transformers and in particular to an improved arrangement of a tapped winding for such transformers.

An object of the present invention is to provide a winding arrangement for a variable ratio transformer which utilizes the insulation strength of disk type windings without the disadvantage of having localized ampere turn unbalance between the high voltage and low voltage windings as the ratio of the transformer is varied.

A further object of the present invention is to provide a winding arrangement for a variable ratio transformer in which the losses resulting from stray flux are minimized.

A still further object of the present invention is to provide a winding arrangement for a variable ratio transformer in which the impedance of the tapped winding varies only slightly throughout the complete tap range.

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with the drawings in which:

Fig. 1 is a diagrammatic view of a variable ratio transformer embodying the improved winding arrangement;

Fig. 2 is a schematic view in elevation of the core and winding assembly shown in Fig. 1;

Fig. 3 is a schematic view of the variable ratio transformer embodying this invention;

Fig. 4 is an enlarged fragmentary plan view of a winding assembly of this invention illustrating the position of the tap leads and winding terminals;

Fig. 5 illustrates diagrammatically a modification of the variable ratio transformer shown in Fig. 1 which is employed if the transformer is to be delta connected; and

Fig. 6 is a schematic view of the modified transformer of this invention.

Referring to the drawings and particularly to Fig. 1, the variable ratio transformer 11 illustrated therein comprises generally a high voltage winding 12, a low voltage Winding 13, a magnetic core 14, and a tap changing switch 15. The high voltage winding 12 is connected between terminals 16 and 17, and the low voltage winding 13 between terminals 18 and 19 of the transformer. The tap changing switch 15 is employed to vary the output voltage of transformer 11 in steps according to standard practice. An additional switch 21 is employed in connection with the low voltage winding 13 to effect changes in voltage both above and below a predetermined value.

The construction and position of the turns in low voltage Winding 13 may be readily seen by referring to Figs. 2 and 3 which illustrate schematically the improved winding arrangement.

As shown in Fig. 3, low voltage winding 13 is disposed on an insulating mold 22 positioned around the center leg 23 of magnetic core 14, with the high voltage winding 12 surrounding the low voltage winding 13. The low voltage winding 13 includes a cylindrical portion 24 and a second portion comprising a plurality of serially connected disk coils 25 which define a disk winding 26. The cylindrical portion 24 is wound helically with respect to the axis of insulating mold 22 which surrounds the core leg 23. The disk portion 26 of the low voltage winding 13 is positioned coaxially with respect to the cylindrical portion 24.

The cylindrical portion 24 comprises a tapped section 27 and an untapped section 28. The untapped section 28 as shown comprises two groups of coils 28a and 28b disposed respectively at opposite ends 30 and 31 of the insulating mold 22, with the tapped section 27 disposed centrally on the mold 22 and intermediate the groups 28a and 28b. However, it should be understood that the two groups of untapped coils 28a and 28b may be disposed adjacent to each other at one end of the mold 22 with the tapped section 27 disposed at the other end of the insulating mold. Alternately, the cylindrical coil portion 24 of the low voltage winding 13 may be wound in two layers with the tapped section 27 forming the first layer and the unstapped section 28 forming the second layer.

The cylindrical portion 24 and the disk portion 26 are connected in series as shown in Figs. 1, 2 and 3, the tapped section 27 being positioned at the grounded end of low voltage winding 13, while one end 32 of the disk winding 26 serves as the line terminal of the low voltage winding 13. The low voltage winding 13 thus extends from the line terminal 18 of the transformer through the entire disk winding portion 26, then through the two groups of cylindrical coils 28a and 28b of the untapped section 28, then through the tapped section 27 and the tap changing switch 15 to ground terminal 19 of the transformer.

If it is desired to vary the voltage of transfonner 11 above and below a predetermined value, means may be provided which operates to tap out a predetermined portion of the low voltage winding 13. As shown in the preferred embodiment, this means comprises auxiliary switch 21 which is basically a single pole double throw type switch.- One end 35 of the tapped cylindrical section 27 is connected to the movable contact 36 of auxiliary switch 21 by means of conductor 37, and the two stationary contacts 38 and 39 of the auxiliary switch 21 are connected respectively to the opposite ends 40 and 41 of the untapped cylindrical section 28 by means of conductors 42 and 43. In one position of the switch 21 the untapped cylindrical section 23 therefore is connected in series between the tapped cylindrical section 27 and the disk coil portion 26 of the winding 13, and in the other position the untapped section 28 of the cylindrical portion 24 is bypassed completely.

The tapped section 27 of the low voltage winding 13 as shown is provided with eight taps 45a through 4512 which are connected respectively to the stationary contacts 46a through 46/1 of the tap changing switch 15 by means of conductors 47a through 47h. The remaining stationary contact 46 is connected to contact 39 of the auxiliary switch 21 by means of conductor 48.

The connections '47 from the taps 45 to the stationary contacts 46 of the tap changing switch 15 may be disposed between the cylindrical portion 24 and the disk portion 26 of the low voltage winding 13 as shown in Fig. 4. The connections 37, 42 and 43 from the terminals of the cylindrical winding section to the contact members 36, 38 and 39, of the auxiliary switch 21 may also be disposed between the cylindrical portion 24 and disk portion 26 of the low voltage winding 13 as shown in Fig. 4. Other suitable connecting arrangements known in the prior art may also be employed.

The embodiment of the transformer shown diagrammatically in Fig. 5 and schematically in Fig. 6 is em- 3 ployed if both terminals of the transformer are to be connected to a line conductor as in the case of a delta circuit arrangement. The physical position of the coils in both the cylindrical portion 50 and disk portion'51 of the winding 52 are similar to the arrangement previously described and illustrated in Fig. 3. However, as shown in Figs. 5 and 6, the cylindrical portion 50 is disposed circuitwise at the center of the winding 52 and 51b of the winding 52 are therefore positioned adjacent i to the line terminals so that the winding is better able to withstand surge voltages which result for example as a result of lightning striking the lines which are connected to the transformer.

The connections between the sections of the winding 1..

52 and to the auxiliary switch 59 are shown in Fig. 6. These connections and the connections from the contacts 58 of the tap changing switch '56 to the taps 60 on the cylindrical portion 50 may be made as previously described in connection with the embodiment of the transformer illustrated in Figs. 1-4.

It is well known that in the design of transformer winding arrangements the ampere turns per inch of length of the primary and secondary windings should under ideal conditions of construction be equal and opposite. If there is little or no ampere turn unbalance between the windings the leakage flux lines in the space between the high and low voltage winding are parallel to the long direction of the winding. If, however, a portion of one of the windings is tapped out an ampere turn unbalance is obtained between the two windings causing a cross flux which results in higher eddy current losses.

The provision of a winding having a tapped cylindrical section adjacent the core with the remaining portion of the winding comprising a plurality of disk coils surrounding the cylindrical section results in improved operating characteristics for the transformer in that the resulting distortion of flux caused when a portion of the winding is tapped out is less than in known prior art arrangements. The improved arrangement reduces the amount of cross flux and hence eddy current losses because the tap section of the winding is spread axially over a greater length of the coil and hence the ampere turns per inch of length of the primary and secondary winding therefore vary less as sections of the cylindrical portion of the winding are tapped out.

While only two embodiments of the present invention have been illustrated and described it will be apparent to those skilled in the art that modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. A winding assembly for a variable ratio transformer, said assembly comprising an insulating mold adapted to surround a core leg of said transformer, and a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils Wound on said mold to define a helical winding having a tapped section, said second portion comprising a plurality of serially connected disk type coils surrounding said helical winding and defining a disk winding, means connecting said first portion in series with said second portion, and means for connecting one end of said second portion to a line terminal of said transformer.

2. A winding assembly for a variable ratio transformer, said assembly comprising an insulating'mold adapted to surround a core leg of said transformer, and

' a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils wound on said mold to define a helical winding having a tapped section and an untapped section, said second portion comprising a plurality of serially connected disk type coils surrounding said helical winding and defining a disk winding, means connecting said tapped section in series with said untapped section, means connecting said first portion in series with said second portion, and means for connecting one end of said second portion to a line terminal of said transformer.

3. A Winding assembly for a variable ratio transformensaid assembly comprising a cylindrical insulating mold adaptedto surround a core leg of said trans: former, and a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils wound helically on said mold to define a first cylindrical section having a plurality of taps and a second untapped cylindrical section, said second portion comprising a plurality of serially connected disk type coils surrounding said helical winding and defining a disk winding, means for connecting one end of said disk winding to a terminal of said transformer, means connecting the other end of said disk Winding to one end of said second cylindrical section, and means connecting the other end of said second cylindrical section to one end of said first cylindrical section.

34. A winding assembly for a variable ratio transformer, said assembly comprising a cylindrical insulating mold adapted to surround a core leg of said transformer, and a winding having first and second portions,

' said first portion comprising a plurality of coils Wound helically on said mold to define a cylindrical winding having a first section and a second section, said first section being disposed centrally on said insulating mold and having a plurality of taps, said second section being untapped and comprising two serially connected groups of coils disposed at opposite ends of said mold, said second portion comprising a plurality of serially connected disk type coils defining a disk winding surrounding said first and second sections and spaced radially therefrom, means for connecting one end of said disk winding to a terminal of said transformer, and means for connecting the other end of said disk winding to the other terminal of said transformer through said first portion.

5. In a variable ratio transformer, having a line terminal and a ground terminal, a tap. switch with a plurality of stationary contacts and movable contacts, and a mag. netic core, a winding assembly for said transformer comprising; a cylindrical insulating mold disposed on said core, and a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils wound helically on said mold to define a cylindrical winding having a first sectiond and a second section, said first section having a plurality of taps, said second section being untapped, said second portion comprising a plurality of serially connected disk coils defining a disk winding surrounding said cylindrical winding, means connecting one end of said disk winding to said line terminal, means connecting the other end of said disk winding to one end of said second section, means connecting the other end of said second section to one end bination a line terminal, a ground terminal, a tap changing switch having a plurality of stationary contacts and movable contacts, an auxiliary switch, and a winding assembly, said winding assembly comprising a cylindrical insulating mold disposed on said core, and a winding having first and second coaxially disposed portions spaced radially outward with respect to the axis of said mold, said first portion comprising a plurality of coils wound helically on said mold to define a cylindrical winding having a first section and a second section, said first section having a plurality of taps connected respectively to said plurality of stationary contacts, said second section comprising two groups of coils spaced axially on said mold on either side of said first section, means connecting said groups in series, said second portion comprising a plurality of serially connected disk type coils defining a disk Winding surrounding said cylindrical winding, means connecting one end of said disk winding to said line terminal, means including said auxiliary switch for selectively connecting said first section in series with said disk winding directly or through said second section, and means for connecting said taps to said ground terminal through said movable contacts of said tap changing switch.

7. A winding assembly for a variable ratio transformer, said assembly comprising a cylindrical insulating mold adapted to surround a core leg of said transformer, and a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils wound helically on said mold to define a first cylindrical section having a plurality of taps and a second untapped cylindrical section, said second portion comprising a disk winding having first and second sections each comprising a plurality of serially connected disk type coils, means for connecting one end of each said section of said disk winding to a terminal of said transformer, means for connecting said cylindrical sections in series, and means for connecting said first and second sections of said disk winding in series through said serially connected cylindrical sections.

8. A winding assembly for a variable ratio transformer, said assembly comprising a cylindrical insulating mold adapted to surround a core leg of said transformer, and a winding having first and second portions, said first portion comprising a plurality of coils wound helically on said mold to define a cylindrical Winding having a first section and a second section, said first section being disposed centrally on said insulating mold and having a plurality of taps, said second section being untapped and comprising two groups of cylindrical coils disposed at opposite ends of said mold, said second portion comprising a plurality of disk type coils defining a disk winding having first and second sections, means for connecting said first and second sections of said first portion in series, means for connecting one end of said first portion to a line terminal of said transformer through said first section of said disk winding, and means for connecting the other end of said first portion to the other line terminal of said transformer through said second section of said disk winding.

9. In a variable ratio tranformer, a pair of line terminals, a tap changing switch having a plurality of stationary contacts and movable contacts, and a magnetic core; a winding assembly for said transformer comprising a cylindrical insulating mold disposed on said core, and a winding having first and second coaxially disposed radially spaced portions, said first portion comprising a plurality of coils wound helically on said mold to define a cylindrical Winding having a first section and a second section,

said first section having a plurality of taps connected to said stationary contacts, said second section being untapped, said second portion comprising a plurality of disk coils defining a disk winding having first and second sections surrounding said cylindrical winding, means connecting one end of each said section of said disk winding to said line terminals, means connecting said first and second sections of said cylindrical winding in series, means connecting one end of said serially connected cylindrical sections to the other end of said first section of said disk winding, and means connecting said other end of said second section of said disk winding to said movable contacts of said tap changing switch.

10. A variable ratio transformer comprising in combination a pair of line terminals, a tap changing switch having a plurality of stationary contacts and movable contacts, an auxiliary switch, and a winding assembly, said winding assembly comprising a cylindrical insulating mold disposed on said core, and a winding having first and second coaxially disposed portions spaced radially outward with respect to the axis of said mold, said first portion comprising a plurality of coils wound helically on said mold to define a cylindrical winding having a first section and a second section, said first section having a plurality of taps connected respectively to said stationary contacts, said second section comprising two serially connected groups of coils spaced axially on said mold on either side of said first tapped section, said second portion comprising a plurality of disk type coils defining a disk winding having first and second sections, means connecting one end of each said sections of said disk winding to said line terminals, means connecting the other end of one of said sections of said disk winding to said movable contacts, and means including said auxiliary switch for selectively connecting said first tapped section of said cylindrical winding to said first section of said disk winding directly or through said second untapped section of said cylindrical winding.

11. A winding assembly for a variable ratio transformer comprising an insulating mold adapted to surround a leg of said transformer and a winding having a pair of concentrically disposed radially spaced inner and outer portions, said inner portion comprising a plurality of coils wound helically on said insulating mold to define a helical winding having a first section provided with a plurality of electrically spaced taps and a second untapped section connected in series with said first section, said outer portion comprising a disk winding having a plurality of serially connected disk coils, means for connecting said inner and outer portions in series between a pair of terminals of said transformer including means connecting one end of said outer portion to the line terminal of said pair of terminals.

References Cited in the file of this patent UNITED STATES PATENTS 2,757,347 Pozaryski July 31, 1956 

